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Is gravity stronger, weaker or the same at the north and south poles compared to the equator? If so, why?
Question Date: 2004-05-07
Answer 1:

In order to answer your question we are going to make some assumptions until we build to the final answer.

If the Earth were perfectly spherical, not rotating, and had no interactions with the sun or the moon, then the force of gravity on an object would be the same everywhere on the earth's surface using Newton's Law of Gravitation. Newton's Law says that the force of gravity is equal to a gravitational constant (G) times the product of the two masses (M and m) divided by the distance between the centers of mass for both objects (r) squared. Mathematically this relation looks like
F = G M m /r2.
But since the Earth is rotating,the radius of the Earth is larger near the equator than near the poles, so the force of gravity at the equator would be less than at the poles. If you add into this situation the effect of tides caused by the moon and sun, the difference can become a little larger.

We can calculate what this difference would be. Let's call the equatorial radius 6378140 m, and the polar radius 6356752 m
(check this out at the following site):
Earth radius .

Using a gravitational constant of 6.67*10-11 Nm2/kg2, and a mass of the earth of 6*1024 kg, let's calculate the gravitational force on a 70 kg (about 155 lbs) person at both the equator and the poles.

At the equator the force of gravitational attraction is 689 N. At the poles the force of gravitational attraction is 693 N.

So, even though there is a difference gravity, it is not noticeable to humans since the difference is about half a percent.

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